Jack Brown on YouTube does AQA videos for C1, C2, and D1/M1/S1 as well all A2 modules - he's really good. As far as tips are concerned, as long as you keep on top of homework and you've got a fairly good GCSE grade, AS Maths will probably be an easy ride. Core 1 is basically GCSE knowledge with a few new concepts added in.

When you start C2, try to get a grip of the trigonometric identities as soon as possible, as you'll be expected to know these in your exam. Try to keep a seperate page in your notes and add all the identities (e.g. cos^2x + sin^2x = 1) in as soon as you learn them. This way you can look back during revision and they'll all be there for you.

ALSO, when you're completing questions from a textbook in your notes, WRITE DOWN THE WHOLE QUESTION!!! Don't just write your answers. This will be soooo helpful when you look back to revise.

And finally, PAST PAPERS! Do as many as you can so that you can get a feel of what kinds of questions the exams tend to ask, and to practice timing.